Near-field RF charging pad with multi-band antenna element with adaptive loading to efficiently charge an electronic device at any position on the pad

ABSTRACT

An example radio frequency (RF) charging pad includes: at least one processor for monitoring an amount of energy that is transferred from the RF charging pad to an RF receiver of an electronic device. The pad also includes: one or more transmitting antenna elements that are in communication with the processor for transmitting RF signals to the RF receiver. In some embodiments, each respective transmitting antenna element includes: (i) a conductive line forming a meandered line pattern; (ii) a first terminal of the conductive line for receiving current at one or more frequencies controlled by the processor; and (iii) one or more adaptive load terminals coupled with a plurality of respective components that allows for modifying an impedance value at each of the adaptive load terminals. In some embodiments, the processor adaptively adjusts the frequency and/or the impedance value to optimize the amount of energy that is transferred from the one or more transmitting antenna elements to the RF receiver.

RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. Non-Provisional patent application Ser. No. 15/424,552, filed Feb. 3, 2017, entitled “Near-Field RF Charging Pad With Adaptive Loading To Efficiently Charge An Electronic Device At Any Position On The Pad” which claims priority to U.S. Provisional Application Ser. No. 62/433,227 filed Dec. 12, 2016, the entire contents of which are incorporated herein by reference in their entireties.

This application is related to U.S. patent application Ser. No. 15/269,729, filed Sep. 19, 2016, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The embodiments herein generally relate to antennas used in wireless power transmission systems and, more specifically, to a near-field RF charging pad with adaptive loading to efficiently charge an electronic device at any position on the pad.

BACKGROUND

Conventional charging pads utilize inductive coils to generate a magnetic field that is used to charge a device. Users typically must place the device at a specific position on the charging pad and are unable to move the device to different positions on the pad, without interrupting or terminating the charging of the device. This results in a frustrating experience for many users as they may be unable to locate the device at the exact right position on the pad in which to start charging their device.

SUMMARY

Accordingly, there is a need for wireless charging systems (e.g., RF charging pads) that include adaptive antenna elements that are able to adjust energy transmission characteristics (e.g., impedance and frequency for a conductive line of a respective antenna element) so that the charging pad is capable of charging a device that is placed at any position on the pad. In some embodiments, these charging pads include one or more processors that monitor energy transferred from the transmitting antenna elements (also referred to herein as RF antenna elements or antenna elements) and to a receiver of an electronic device to be charged, and the one or more processors optimize the energy transmission characteristics to maximize energy transfer at any position on the charging pad. Some embodiments may also include a feedback loop to report received power at the receiver to the one or more processors. Such systems and methods of use thereof help to eliminate user dissatisfaction with conventional charging pads. By monitoring transferred energy, such systems and methods of use thereof help to eliminate wasted RF power transmissions by ensuring that energy transfer is maximized at any point in time and at any position at which a device may be placed on an RF charging pad, thus eliminating wasteful transmissions that may not be efficiently received.

(A1) In accordance with some embodiments, a radio frequency (RF) charging pad is provided. The RF charging pad includes: at least one processor for monitoring an amount of energy that is transferred from the RF charging pad to an RF receiver of an electronic device. The RF charging pad also includes: one or more antenna elements that are in communication with the one or more processors for transmitting RF signals to the RF receiver of the electronic device. In some embodiments, each respective antenna element includes: (i) a conductive line forming a meandered line pattern; (ii) a first terminal at a first end of the conductive line for receiving current that flows through the conductive line at a frequency controlled by the one or more processors; and (iii) a second terminal, distinct from the first terminal, at a second end of the conductive line, the second terminal coupled with a component that is controlled by the at least one processor and allows for modifying an impedance value at the second terminal. In some embodiments, the at least one processor is configured to adaptively adjust the frequency and/or the impedance value to optimize the amount of energy that is transferred from the one or more antenna elements to the RF receiver of the electronic device.

(A2) In accordance with some embodiments, a method is also provided that is used to charge an electronic device through radio frequency (RF) power transmission. The method includes: providing a transmitter comprising at least one RF antenna. The method also includes: transmitting, via at the least one RF antenna, one or more RF signals and monitoring an amount of energy that is transferred via the one or more RF signals from the at least one RF antenna to an RF receiver. The method additionally includes: adaptively adjusting a characteristic of the transmitter to optimize the amount of energy that is transferred from the at least one RF antenna to the RF receiver.

(A3) In accordance with some embodiments, a radio frequency (RF) charging pad is provided. The RF charging pad includes: one or more processors for monitoring an amount of energy that is transferred from the RF charging pad to an RF receiver of an electronic device. The RF charging pad also includes: one or more transmitting antenna elements that are configured to communicate with the one or more processors for transmitting RF signals to the RF receiver of the electronic device. In some embodiments, each respective antenna element includes: (i) a conductive line forming a meandered line pattern; (ii) an input terminal at a first end of the conductive line for receiving current that flows through the conductive line at a frequency controlled by the one or more processors; and (iii) a plurality of adaptive load terminals, distinct from the input terminal and distinct from each other, at a plurality of positions of the conductive line, each respective adaptive load terminal of the plurality of adaptive load terminals coupled with a respective component that is configured to be controlled by the one or more processors and is configured to allow modifying a respective impedance value at the respective adaptive load terminal. In some embodiments, the one or more processors are configured to adaptively adjust at least one of the frequency and a respective impedance value at one or more of the plurality of adaptive load terminals to optimize the amount of energy that is transferred from the one or more transmitting antenna elements to the RF receiver of the electronic device.

(A4) In accordance with some embodiments, a method is also provided that is used to charge an electronic device through radio frequency (RF) power transmission. The method includes: providing a charging pad that includes a transmitter comprising one or more RF antennas. In some embodiments, each RF antenna includes: (i) a conductive line forming a meandered line pattern; (ii) an input terminal at a first end of the conductive line for receiving current that flows through the conductive line at a frequency controlled by one or more processors; and (iii) a plurality of adaptive load terminals, distinct from the input terminal and distinct from each other, at a plurality of positions of the conductive line, each respective adaptive load terminal of the plurality of adaptive load terminals coupled with a respective component that is controlled by the one or more processors and allows for modifying a respective impedance value at the respective adaptive load terminal. The method also includes: transmitting, via the one or more RF antennas, one or more RF signals, and monitoring an amount of energy that is transferred via the one or more RF signals from the one or more RF antennas to an RF receiver. The method additionally includes: adaptively adjusting a characteristic of the transmitter using the one or more processors of the transmitter to optimize the amount of energy that is transferred from the one or more RF antennas to the RF receiver. In some embodiments, the characteristic is selected from a group consisting of (i) a frequency of the one or more RF signals, (ii) an impedance of the transmitter, and (iii) a combination of (i) and (ii). In some embodiments, the impedance of the transmitter is adaptively adjusted at a respective one or more of the plurality of adaptive load terminals of the one or more RF antennas using the one or more processors of the transmitter.

(A5) In accordance with some embodiments, a non-transitory computer-readable storage medium is provided. The non-transitory computer-readable storage medium includes executable instructions that, when executed by one or more processors that are coupled with a radio frequency (RF) charging pad that includes one or more transmitting antenna elements, cause the one or more processors to: monitor an amount of energy that is transferred from the RF charging pad to an RF receiver of an electronic device; and communication with the one or more transmitting antenna elements for transmitting RF signals to the RF receiver of the electronic device. In some embodiments, each respective transmitting antenna element includes: a conductive line forming a meandered line pattern; an input terminal at a first end of the conductive line for receiving current that flows through the conductive line at a frequency controlled by the one or more processors; and a plurality of adaptive load terminals, distinct from the input terminal and distinct from each other, at a plurality of positions of the conductive line, each respective adaptive load terminal of the plurality of adaptive load terminals coupled with a respective component that is configured to be controlled by the one or more processors and is configured to allow modifying a respective impedance value at each respective adaptive load terminal. And the one or more processors further adaptively adjust at least one of the frequency and a respective impedance value at one or more of the plurality of adaptive load terminals to optimize the amount of energy that is transferred from the one or more transmitting antenna elements to the RF receiver of the electronic device.

(A6) In some embodiments of any of A1-A5, the frequency is in a first frequency band, and at least one of the one or more transmitting antenna elements is configured to operate at a second frequency band based on adaptive adjustments, by the one or more processors, to respective impedance values at one or more of the plurality of adaptive load terminals of the at least one transmitting antenna element.

(A7) In some embodiments of any of A1-A6, the RF charging pad includes an input circuit that is coupled with the one or more processors and is configured to provide the current to the input terminal at the first end of the conductive line, wherein the one or more processors are configured to adaptively adjust the frequency by instructing the input circuit to generate the current with a new frequency that is distinct from the frequency.

(A8) In some embodiments of any of A1-A7, the one or more processors are configured to adaptively adjust the frequency by instructing the feeding element to generate the current with a plurality of different frequencies that are determined using predetermined increments.

(A9) In some embodiments of any of A1-A8, a respective conductive line for at least one of the one or more transmitting antenna elements has a respective meandered line pattern that allows the at least one transmitting antenna element to efficiently transmit RF signals having the frequency and/or the new frequency, at least two adjacent segments of the respective conductive line having the respective meandered line pattern have different geometric dimensions relative to each other, and the respective conductive line has a length that remains the same when the at least one transmitting antenna element is configured to transmit RF signals having the frequency and/or the new frequency.

(A10) In some embodiments of any of A1-A9, at least one transmitting antenna element of the one or more transmitting antenna elements has a first segment and a second segment, the first segment including the input terminal, and the at least one transmitting antenna element is configured to: operate at the frequency while the first segment is not coupled with the second segment, and operate at the new frequency while the first segment is coupled with the second segment; and the one or more processors are configured to couple the first segment with the second segment in conjunction with instructing the feeding element to generate the current with the new frequency that is distinct from the frequency.

(A11) In some embodiments of any of A1-A10, the one or more processors are configured to: adaptively adjust the frequency and/or a respective impedance value associated with a first transmitting antenna element of the one or more transmitting antenna elements to cause the first transmitting antenna element to operate in a first frequency band, and adaptively adjust the frequency and/or the respective impedance value associated with a second transmitting antenna element of the one or more transmitting antenna elements to cause the second transmitting antenna element to operate in a second frequency band, wherein the first frequency band is distinct from the second frequency band.

(A12) In some embodiments of any of A1-A11, the electronic device is placed in contact with or close to a top surface of the RF charging pad.

(A13) In some embodiments of any of A1-A12, the respective component is a mechanical relay coupled with the respective adaptive load terminal for switching the respective adaptive load terminal between open and short states, and the impedance value is adaptively adjusted at the respective adaptive load terminal of the respective transmitting antenna element by opening or closing the mechanical relay to switch between an open or short circuit, respectively.

(A14) In some embodiments of any of A1-A12, the respective component is an application-specific integrated circuit (ASIC), and the respective impedance value is adaptively adjusted by the ASIC to within a range of values.

(A15) In some embodiments of any of A1-A14, the one or more processors are configured to: adaptively adjust the frequency and/or the respective impedance value by adaptively adjusting the frequency and a respective impedance value at one or more of the plurality of adaptive load terminals to determine a relative maximum amount of energy that is transferred to the RF receiver of the electronic device, and once the maximum amount of energy is determined, cause each of the one or more transmitting antenna elements to respectively transmit the RF signals at a respective frequency and using a respective impedance value that resulted in the maximum amount of energy transferred to the RF receiver.

(A16) In some embodiments of any of A1-A15, the one or more processors monitor the amount of energy that is transferred to the RF receiver based at least in part on information received from the electronic device, the information identifying energy received at the RF receiver from the RF signals.

(A17) In some embodiments of any of A1-A16, the information received from the electronic device identifying received energy is sent using a wireless communication protocol.

(A18) In some embodiments of any of A1-A17, the wireless communication protocol is bluetooth low energy (BLE).

(A19) In some embodiments of any of A1-A18, the one or more processors monitor the amount of energy transferred based at least in part on an amount of energy that is detected at the respective adaptive load terminal.

Thus, wireless charging systems configured in accordance with the principles described herein are able to charge an electronic device that is placed at any position on the RF charging pad and avoid wasting energy by ensuring that energy transfer is constantly optimized.

In addition, wireless charging systems configured in accordance with the principles described herein are able to charge different electronic devices that are tuned at different frequencies or frequency bands on the same charging transmitter. In some embodiments, a transmitter with a single antenna element can operate at multiple frequencies or frequency bands at the same time or at different times. In some embodiments, a transmitter with multiple antenna elements can operate at multiple frequencies or frequency bands at the same time. That enables more flexibility in the types and sizes of antennas that are included in receiving devices.

Note that the various embodiments described above can be combined with any other embodiments described herein. The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not intended to circumscribe or limit the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the present disclosure can be understood in greater detail, a more particular description may be had by reference to the features of various embodiments, some of which are illustrated in the appended drawings. The appended drawings, however, merely illustrate pertinent features of the present disclosure and are therefore not to be considered limiting, for the description may admit to other effective features.

FIG. 1A is a high-level block diagram of an RF charging pad, in accordance with some embodiments.

FIGS. 1B-1C are high-level block diagrams showing a portion of an RF charging pad, in accordance with some embodiments.

FIG. 1D is a block diagram of a simplified circuit that illustrates energy flow within sections of an antenna element that is transmitting an RF signal, in accordance with some embodiments.

FIG. 2 is a schematic of a transmitting antenna element with two terminals, in accordance with some embodiments.

FIG. 3 is a flow chart of a method of charging an electronic device through radio frequency (RF) power transmission.

FIGS. 4A-4E are schematics showing various configurations for individual antenna elements within an RF charging pad, in accordance with some embodiments.

FIGS. 5A-5D are schematics of an antenna element for an RF receiver, in accordance with some embodiments.

FIG. 6 is a schematic of an RF charging pad with a plurality of transmitting antenna elements (or unit cells), in accordance with some embodiments.

FIG. 7 is a schematic of a transmitting antenna element with a plurality of adaptive loads of an RF charging pad, in accordance with some embodiments.

FIG. 8 is a flow chart of a method of charging an electronic device through radio frequency (RF) power transmission by using at least one RF antenna with a plurality of adaptive loads, in accordance with some embodiments.

FIGS. 9A-9D are schematics showing various configurations for individual antenna elements that can operate at multiple frequencies or frequency bands within an RF charging pad, in accordance with some embodiments.

FIG. 10 is schematic showing an example configuration for an individual antenna element that can operate at multiple frequencies or frequency bands by adjusting the length of the antenna element, in accordance with some embodiments.

In accordance with common practice, the various features illustrated in the drawings may not be drawn to scale. Accordingly, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may not depict all of the components of a given system, method or device. Finally, like reference numerals may be used to denote like features throughout the specification and figures.

DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the various described embodiments. However, it will be apparent to one of ordinary skill in the art that the various described embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure aspects of the embodiments.

FIG. 1A is a high-level block diagram of an RF charging pad, in accordance with some embodiments. As shown in FIG. 1A, some embodiments include a transmission pad 100 (also referred to herein as RF charging pad 100 or RF transmission pad 100). In some embodiments, the RF charging pad 100 includes one or more antenna elements that are each powered/fed by a respective power amplifier switch circuit 103 at a first end and a respective adaptive load terminal 102 at a second end (additional details and descriptions of the one or more antenna elements are provided below in reference to FIGS. 2A-2B).

In some embodiments, the RF charging pad 100 also includes (or is in communication with) a central processing unit 110 (also referred to here as processor 110). In some embodiments, the processor 110 is configured to control RF signal frequencies and to control impedance values at each of the adaptive load terminals 102 (e.g., by communicating with the load pick or adaptive load 106, which may be an application-specific integrated circuit (ASIC), or a variable resister, to generate various impedance values). In some embodiments, the load pick 106 is an electromechanical switch that is placed in either an open or shorted state.

In some embodiments, an electronic device (e.g., a device that includes a receiver 104 as an internally or externally connected component, such as a remote that is placed on top of a charging pad 100 that may be integrated within a housing of a streaming media device or a projector) and uses energy transferred from one or more RF antenna elements of the charging pad 100 to the receiver 104 to charge a battery and/or to directly power the electronic device.

In some embodiments, the RF charging pad 100 is configured with more than one input terminal for receiving power (from power amplifier (PA) 108, FIG. 1A) and more than one output or adaptive load terminal 102. In some embodiments, the adaptive load terminals 102 at a particular zone of the RF charging pad 100 (e.g., a zone that includes antenna elements located underneath a position at which an electronic device (with an internally or externally connected RF receiver 104) to be charged is placed on the charging pad) are optimized in order to maximize power received by the receiver 104. For example, the CPU 110 upon receiving an indication that an electronic device with an internally or externally connected RF receiver 104 has been placed on the pad 100 in a particular zone 105 (the zone 105 includes a set of antenna elements) may adapt the set of antenna elements to maximize power transferred to the RF receiver 104. Adapting the set of antenna elements may include the CPU 110 commanding load pick 106 to try various impedance values for adaptive load terminals 102 that are associated with the set of antenna elements. For example, the impedance value for a particular conductive line at an antenna element is given by the complex value of Z=A+jB (where A is the real part of the impedance value and B is the imaginary part, e.g., 0+j0, 1000+j0, 0+50j, or 25+j75, etc.), and the load pick adjusts the impedance value to maximize the amount of energy transferred from the set of antenna elements to the RF receiver 104. In some embodiments, adapting the set of antenna elements also or alternatively includes the CPU 110 causing the set of antenna elements to transmit RF signals at various frequencies until a frequency is found at which a maximum amount of energy is transferred to the RF receiver 104. In some embodiments, adjusting the impedance value and/or the frequencies at which the set of antenna elements transmits causes changes to the amount of energy transferred to the RF receiver 104. In this way, the amount of energy transferred to the RF receiver 104 is maximized (e.g., to transfer at least 75% of the energy transmitted by antenna elements of the pad 100 to the receiver 104, and in some embodiments, adjusting the impedance value and/frequencies may allow up to 98% of the energy transmitted to be received by the receiver 104) may be received at any particular point on the pad 100 at which the RF receiver 104 might be placed.

In some embodiments, the input circuit that includes the power amplifier 108 can additionally include a device that can change frequencies of the input signal, or a device that can operate at multiple frequencies at the same time, such as an oscillator or a frequency modulator.

In some embodiments, the CPU 110 determines that a maximum amount of energy is being transferred to the RF receiver 104 when the amount of energy transferred to the RF receiver 104 crosses a predetermined threshold (e.g., 75% or more of transmitted energy is received, such as up to 98%) or by testing transmissions with a number of impedance and/or frequency values and then selecting the combination of impedance and frequency that results in maximum energy being transferred to the RF receiver 104 (as described in reference to the adaptation scheme below).

In some embodiments, an adaptation scheme is employed to adaptively adjust the impedance values and/or frequencies of the RF signal(s) emitted from the RF antenna(s) 120 of the charging pad 100, in order to determine which combinations of frequency and impedance result in maximum energy transfer to the RF receiver 104. For example, the processor 110 that is connected to the charging pad 100 tries different frequencies (i.e., in the allowed operating frequency range or ranges) at a given location of the RF charging pad 100 (e.g., a zone or area of the RF charging pad 100 that includes one or more RF antenna elements for transmitting RF signals, such as zone 105 of FIG. 1A) to attempt to adaptively optimize for better performance. For example, a simple optimization either opens/disconnects or closes/shorts each load terminal to ground (in embodiments in which a relay is used to switch between these states), and may also cause RF antennas within the zone to transmit at various frequencies. In some embodiments, for each combination of relay state (open or shorted) and frequency, the energy transferred to the receiver 104 is monitored and compared to energy transferred when using other combinations. The combination that results in maximum energy transfer to the receiver 104 is selected and used to continue to transmitting the one or more RF signals to the receiver 104.

As another example, if five frequencies in the ISM band are utilized by the pad 100 for transmitting radio frequency waves and the load pick 106 is an electromechanical relay for switching between open and shorted states, then employing the adaptation scheme would involve trying 10 combinations of frequencies and impedance values for each antenna element 120 or for a zone of antenna elements 120 and selecting the combination that results in best performance (i.e., results in most power received at receiver 104, or most power transferred from the pad 100 to the RF receiver 104).

The industrial, scientific, and medical radio bands (ISM bands) refers to a group of radio bands or parts of the radio spectrum that are internationally reserved for the use of radio frequency (RF) energy intended for scientific, medical and industrial requirements rather than for communications. In some embodiments, all ISM bands (e.g., 40 MHz, 900 MHz, 2.4 GHz, 5.8 GHz, 24 GHz, 60 GHz, 122 GHz, and 245 GHz) may be employed as part of the adaptation scheme. As one specific example, if the charging pad 100 is operating in the 5.8 GHz band, then employing the adaptation scheme would include transmitting RF signals and then adjusting the frequency at predetermined increments (e.g., 50 MHz increments, so frequencies of 5.75 GHz, 5.755 GHz, 5.76 GHz, and so on). In some embodiments, the predetermined increments may be 5, 10 15, 20, 50 MHz increments, or any other suitable increment.

In some embodiments, the antenna elements 120 of the pad 100 may be configured to operate in two distinct frequency bands, e.g., a first frequency band with a center frequency of 915 MHz and a second frequency band with a center frequency of 5.8 GHz. In these embodiments, employing the adaptation scheme may include transmitting RF signals and then adjusting the frequency at first predetermined increments until a first threshold value is reached for the first frequency band and then adjusting the frequency at second predetermined increments (which may or may not be the same as the first predetermined increments) until a second threshold value is reached for the second frequency band. For example, the antenna elements 120 may be configured to transmit at 902 MHz, 915 MHz, 928 MHZ (in the first frequency band) and then at 5.795 GHz, 5.8 GHz, and 5.805 GHz (in the second frequency band). Additional details regarding antenna elements that are capable of operating at multiple frequencies are provided below in reference to FIGS. 9A-9D and 10.

Turning now to FIGS. 1B-1C, high-level block diagrams showing a portion of an RF charging pad are illustrated, in accordance with some embodiments.

FIG. 1B shows a schematic of a single TX antenna 120 (which may be a part of an array of such antennas, all forming the charging pad 100 that is shown in FIG. 1A). (In some embodiments, the TX antenna 120 is also referred to as a TX antenna element 120). In some circumstances, an RF receiving unit/antenna (RX) (or a device that includes the receiving unit 104 as an internally or externally connected component) is placed on top of a portion of the pad 100 that includes the TX antenna 120 (which includes a conductive line that forms a meandered line arrangement, as shown in FIG. 1B).

In some embodiments, the receiver 104 has no direct contact to a metallic conductive line of the single TX antenna 120 and is just coupled (i.e. in near-field zone) to the TX antenna 120.

In some embodiments, the TX antenna 120 has two or more terminals (or ports) that are labeled as 121 (which may be a respective one of the terminals 102 of FIG. 1A) and 123 (which may be connected to a respective one of the PA switch circuits 103 of FIG. 1A) in FIG. 1B. In some embodiments, the source of power (from the power amplifier or PA) is connected to terminal 123 and an adaptive load (e.g., an electromechanical switch or ASIC) is connected to terminal 121. In some embodiments, the adaptive load is formed generally as a complex impedance which may have both real and imaginary parts (i.e., a complex adaptive load can be formed using active devices (e.g., integrated circuits or chips made of transistors) or passive devices formed by inductors/capacitors and resistors). In some embodiments, the complex impedance is given by the formula Z=A+jB (e.g., 0+j0, 100+j0, 0+50j, and etc.), as discussed above.

In some embodiments, the receiver 104 may also be considered as a third terminal. To eliminate wasted energy, the receiver 104 should be configured to absorb a maximum amount (e.g., 75% or more, such as 98%) of the induced power that travels from terminal 123 and towards terminal 121. In some embodiments, processor 110 is connected to the receiver 104 through a feedback loop (e.g., by exchanging messages using a short-range communication protocol, such by BLUETOOTH low energy (BLE) to exchange messages). In some alternative embodiments, the feedback loop from the receiver back to the CPU at the transmitter may utilize a same frequency band as the power transmission signals transmitted by the pad 100, rather than using a separate communication protocol and/or a different frequency band.

In some embodiments, the feedback loop and messages exchanged may be used to indicate an amount of energy received or alternatively or additionally may indicate an increase or decrease in the amount of energy received as compared to previous measurements. In some embodiments, the processor 110 monitors the amount of energy received by the receiver 104 at certain points in time and controls/optimizes the adaptive load to maximize the power transferred from terminal 123 to terminal 121. In some embodiments, monitoring the amount of energy transferred includes one or both of (i) receiving information from the receiver 104 (or a component of an electronic device in which the receiver 104 is located) that indicates an amount of energy received by the receiver 104 at a certain point in time and (ii) monitoring an amount of energy that remains in the conductive line at terminal 121 (instead of having been absorbed by the receiver 104). In some embodiments, both of these monitoring techniques are utilized while, in other embodiments, one or the other of these monitoring techniques is utilized.

In some embodiments, the receiver 104 (i.e., an electronic device that includes the receiver 104 as an internally or externally connected component) may be placed anywhere on top of the charging pad 100 (i.e., partially or fully covering the conductive line that forms a meandered pattern on a respective antenna element 120) and the processor 110 will continue to monitor the amount of energy transferred and make needed adjustments (e.g., to impedance and/or frequency) to maximize the energy transferred to the receiver 104.

To help illustrate operation of the charging pad 100 and the antenna elements 120 included therein, the transmitting antenna element 120 shown in FIG. 1B as divided into two sections: 1) section 125 starts at the terminal 123 of the antenna element 120 and extends to an edge of the receiver 104; and 2) section 127 is formed by the rest of the transmitting antenna element 120 and the terminal 121. The blocks are described in more detail below with respect to FIG. 1C. It should be understood that sections 125 and 127 are functional representations used for illustrative purposes, and they are not intended to designate a specific implementation that partitions an antenna element into separate sections.

Turning now to FIG. 1C, a block diagram of the TX antenna 120 is shown. In some embodiments, an effective impedance value (Z_(effective)), starting from a point that divides sections 125 and 127 and ending at the TX antenna 120's connection to the adaptive load 106 (e.g., terminal 121) will change based on location of the receiver 104 on the TX antenna 120 and based on a selected load provided by adaptive load 106 at the terminal 121. In some embodiments, the selected load is optimized by the adaptive load 106 (in conjunction with the processor 110, FIG. 1A) to tune Z_(effective) in such a way that the energy transferred between terminal 123 and the receiver 104 reaches a maximum (e.g., 75% or more of energy transmitted by antenna elements of the pad 100 is received by the RF receiver 104, such as 98%), while energy transfer may also stay at a minimum from terminal 123 to terminal 121 (e.g., less than 25% of energy transmitted by antenna elements of the pad 100 is not received by the RF receiver 104 and ends up reaching terminal 121 or ends up being reflected back, including as little as 2%).

In embodiments in which an electromechanical switch (e.g., a mechanical relay) is used to switch between open and shorted states, moving the switch from the open to the shorted state (e.g., shorted to a ground plane) for a particular antenna element 120 causes the impedance value, Z_(effective), at a respective terminal 121 for that particular antenna element 120 to drop to a value close to 0 (alternatively, switching from the shorted to the open state causes the impedance value to jump close to a value close to infinity). In some embodiments, the frequency adaptation scheme discussed above in reference to FIG. 1A is employed to test various combinations of impedance values and RF signal frequencies, in order to maximize energy transferred to an RF receiver (e.g., receiver 104, FIGS. 1A-1C). In some embodiments, an integrated circuit (IC or chip) may be used instead of an electromechanical switch as the adaptive load 106. In such embodiments, the adaptive load 106 is configured to adjust the impedance value along a range of values, such as between 0 and infinity. In some embodiments, the IC may be formed by adaptive/reconfigurable RF active and/or passive elements (e.g., transistors and transmission lines) that are controlled by firmware of the IC (and/or firmware executing on the CPU 110 that controls operation of the IC). In some embodiments, the impedance produced by the IC, and controlled through firmware and based on information from the feedback loop (discussed above in reference to FIG. 1A), may be changed to cover any load values selected from a Smith Chart (or the IC may be designed to produce certain loads covering a portion of values form the Smith Chart). A Smith Chart may be sampled and stored in a memory (e.g., as a lookup table) that is accessible by the processor 110, and the processor 110 may perform lookups using the stored Smith Chart to determine various impedance values to test. For example, the integrated circuit may be configured to select a predetermined number of complex values (e.g., 5j to 10j, 100+0j, or 0+50j, etc.) for the impedance value to test in combination with various RF transmission frequencies, in order to locate a combination of values that optimizes energy transferred to the receiver 104 (examples of maximized energy transfer are discussed above).

In some other embodiments, a transmitter or charging pad with more than one antenna elements 120 of FIG. 1B with one adaptive load 106 may be configured to operate in two or more distinct frequency bands respectively at the same time. For example, a first antenna element operates at a first frequency or frequency band, a second antenna element operates at a second frequency or frequency band, and a third antenna element operates at a third frequency or frequency band, and a fourth antenna element operates at a fourth frequency or frequency band, and the four frequency bands are distinct from each other. A transmitter with two or more antenna elements 120 therefore can be used as a multi-band transmitter.

FIG. 1D is a block diagram of a simplified circuit that illustrates energy flow within sections of an antenna element that is transmitting an RF signal, in accordance with some embodiments. The references to part1 and part2 in FIG. 1D refer to sections illustrated in FIGS. 1B and 1C, in particular, part1 corresponds to section 125 and part2 corresponds to section 127.

As shown in FIG. 1D, the effective impedance (Z_(effective)) for a transmitting antenna element 120 is formed by the portion of the conductive line that is after the receiver 104 (which, in some embodiments, forms a meandered line pattern as discussed in more detail below) and the adaptive load (labelled to as section 127 in FIGS. 1B and 1C). In some embodiments, by optimizing, the load Z_(effective) will be tuned so the energy transferred from PA to the receiver 104 is maximized; and, the energy remaining in the conductive line by the time it reaches the adaptive load is minimized (as discussed above).

FIG. 2 is a schematic of an antenna element with two terminals, in accordance with some embodiments. As shown in FIG. 2, an input or first terminal of the antenna element 120 (also described as terminal 123 in reference to FIGS. 1B-1D above) is connected with a power amplifier 108 and an output or second terminal (also described as terminal 121 in reference to FIGS. 1B-1D above) is connected with a component 106 that allows for configuring an adaptive load. Stated another way, in some embodiments, the antenna element 120 is fed by the power amplifier 108 from the first terminal and the antenna element 120 is also terminated at a second terminal at an adaptive load (for example, the mechanical relay that switches between shorted and open states).

In some embodiments, the charging pad 100 (FIG. 1A) is made of single-layer or multi-layer copper antenna elements 120 with conductive lines that form a meandered line pattern. In some embodiments, each of these layers has a solid ground plane as one of its layers (e.g., a bottom layer). One example of a solid ground plane is shown and labelled for the transmitting antenna element shown in FIG. 2.

In some embodiments, the RF charging pad 100 (and individual antenna elements 120 included therein) is embedded in a consumer electronic device, such as a projector, a laptop, or a digital media player (such as a networked streaming media player, e.g. a ROKU device, that is connected to a television for viewing streaming television shows and other content). For example, by embedding the RF charging pad 100 in a consumer electronic device, a user is able to simply place a peripheral device, such as a remote for a projector or a streaming media player (e.g., the remote for the projector or streaming media player includes a respective receiver 104, such as the example structures for a receiver 104 shown in FIGS. 5A-5D), on top of the projector or the streaming media player and the charging pad 100 included therein will be able to transmit energy to a receiver 104 that is internally or externally connected to the remote, which energy is then harvested by the receiver 104 for charging of the remote.

In some embodiments, the RF charging pad 100 may be included in a USB dongle as a standalone charging device on which a device to be charged is placed. In some embodiments, the antenna elements 120 may be placed near a top surface, side surfaces, and/or a bottom surface of the USB dongle, so that a device to be charged may be placed at various positions that contact the USB dongle (e.g., a headphone that is being charged might sit on top of, underneath, or hang over the USB dongle and would still be able to receive RF transmissions from the embedded RF charging pad 100).

In some embodiments, the RF charging pad 100 is integrated into furniture, such as desks, chairs, countertops, etc., thus allowing users to easily charge their devices (e.g., devices that includes respective receivers 104 as internally or externally connected components) by simply placing them on top of a surface that includes an integrated RF charging pad 100.

Turning now to FIG. 3, a flow chart of a method 300 of charging an electronic device through radio frequency (RF) power transmission is provided. Initially, a transmitter is provided 302 that includes at least one RF antenna (e.g., antenna element 120, FIGS. 1B-1D and 2) for transmitting one or more RF signals or waves, i.e., an antenna designed to and capable of transmitting RF electromagnetic waves. In some embodiments, an array of RF antenna elements 120 are arranged adjacent to one another in a single plane, in a stack, or in a combination of thereof, thus forming an RF charging pad 100. In some embodiments, the RF antenna elements 120 each include an antenna input terminal (e.g., the first terminal 123 discussed above in reference to FIG. 2) and an antenna output terminal (e.g., the second terminal 121 discussed above in reference to FIG. 2).

In some embodiments, a receiver (e.g., receiver 104, FIGS. 1A-1D) is also provided 304. The receiver also includes one or more RF antennas for receiving RF signals 310. In some embodiments, the receiver includes at least one rectenna that converts 318 the one or more RF signals into usable power to charge a device that includes the receiver 104 as an internally or externally connected component. In use, the receiver 104 is placed 306 within a near-field radio frequency distance to the at least one antenna. For example, the receiver may be placed on top of the at least one RF antenna or on top of a surface that is adjacent to the at least one RF antenna, such as a surface of a charging pad 100.

One or more RF signals are then transmitted 308 via at the least one RF antenna. The system is then monitored 312/314 to determine the amount of energy that is transferred via the one or more RF signals from the at least one antenna to a RF receiver (as is also discussed above). In some embodiments, this monitoring 312 occurs at the transmitter, while in other embodiments the monitoring 314 occurs at the receiver which sends data back to the transmitter via a back channel (e.g., over a wireless data connection using WIFI or BLUETOOTH). In some embodiments, the transmitter and the receiver exchange messages via the back channel, and these messages may indicate energy transmitted and/or received, in order to inform the adjustments made at step 316.

In some embodiments, a characteristic of the transmitter is adaptively adjusted 316 to attempt to optimize the amount of energy that is transferred from the at least one RF antenna to the receiver. In some embodiments, this characteristic is a frequency of the one or more RF signals and/or an impedance of the transmitter. In some embodiments, the impedance of the transmitter is the impedance of the adjustable load. Also in some embodiments, the at least one processor is also configured to control the impedance of the adaptive load. Additional details and examples regarding impedance and frequency adjustments are provided above.

In some embodiments, the transmitter includes a power input configured to be electrically coupled to a power source, and at least one processor (e.g., processor 110, FIGS. 1A-1B) configured to control at least one electrical signal sent to the antenna. In some embodiments, the at least one processor is also configured to control the frequency of the at least one signal sent to the antenna.

In some embodiments, the transmitter further comprises a power amplifier electrically coupled between the power input and the antenna input terminal (e.g., PA 108, FIGS. 1A, 1C, 1D, and 2). Some embodiments also include an adaptive load electrically coupled to the antenna output terminal (e.g., terminal 121, FIGS. 1A-1C and 2). In some embodiments, the at least one processor dynamically adjusts the impedance of the adaptive load based on the monitored amount of energy that is transferred from the at least one antenna to the RF receiver. In some embodiments, the at least one processor simultaneously controls the frequency of the at least one signal sent to the antenna.

In some embodiments, each RF antenna of the transmitter includes: a conductive line forming a meandered line pattern, a first terminal (e.g., terminal 123) at a first end of the conductive line for receiving current that flows through the conductive line at a frequency controlled by one or more processors, and a second terminal (e.g., terminal 121), distinct from the first terminal, at a second end of the conductive line, the second terminal coupled to a component (e.g., adaptive load 106) controlled by the one or more processors and that allows for modifying an impedance value of the conductive line. In some embodiments, the conductive line is disposed on or within a first antenna layer of a multi-layered substrate. Also in some embodiments, a second antenna is disposed on or within a second antenna layer of the multi-layered substrate. Finally, some embodiments also provide a ground plane disposed on or within a ground plane layer of the multi-layered substrate.

FIGS. 4A-4E are schematics showing various configurations for individual antenna elements within an RF charging pad, in accordance with some embodiments. As shown in FIGS. 4A-4E, an RF charging pad 100 (FIG. 1A) may include antenna elements 120 that are made using different structures.

For example, FIGS. 4A-4B show examples of structures for an antenna element 120 that includes multiple layers that each include conductive lines formed into meandered line patterns. The conductive lines at each respective layer may have the same (FIG. 4B) or different (FIG. 4A) widths (or lengths, or trace gauges, or patterns, spaces between each trace, etc.) relative to other conductive lines within a multi-layer antenna element 120. In some embodiments, the meandered line patterns may be designed with variable lengths and/or widths at different locations of the pad 100 (or an individual antenna element 120), and the meandered line patterns may be printed on more than one substrate of an individual antenna element 120 or of the pad 100. These configurations of meandered line patterns allow for more degrees of freedom and, therefore, more complex antenna structures may be built that allow for wider operating bandwidths and/or coupling ranges of individual antenna elements 120 and the RF charging pad 100.

Additional example structures are provided in FIGS. 4C-4E: FIG. 4C shows an example of a structure for an antenna element 120 that includes multiple layers of conductive lines forming meandered line patterns that also have sliding coverage (in some embodiments, respective meandered line patterns may be placed in different substrates with just a portion of a first meandered line pattern of a respective substrate overlapping the a second meandered line pattern of a different substrate (i.e., sliding coverage), and this configuration helps to extend coverage throughout width of the antenna structure); FIG. 4D shows an example of a structure for an antenna element 120 that includes a conductive line having different lengths at each turn within the meandered line pattern (in some embodiments, using different lengths at each turn helps to extend coupling range of the antenna element 120 and/or helps add to the operating bandwidth of the RF charging pad 100); and FIG. 4E shows an example of a structure for an antenna element 120 that includes a conductive line that forms two adjacent meandered line patterns (in some embodiments, having a conductive line that forms two adjacent meandered line patterns helps to extend width of the antenna element 120). All of these examples are non-limiting and any number of combinations and multi-layered structures are possible using the example structures described above.

FIGS. 5A-5D are schematics of an antenna element for an RF receiver, in accordance with some embodiments. In particular FIGS. 5A-5D show examples of structures for RF receivers (e.g., receiver 104, FIGS. 1A-1D and 2), including: (i) a receiver with a conductive line that forms meandered line patterns (the conductive line may or may not be backed by solid ground plane or reflector), as shown in FIGS. 5A (single-polarity receiver) and 5B (dual-polarity receiver). FIGS. 5C-5D show additional examples of structures for an RF receiver with dual-polarity and a conductive line that forms a meandered line pattern. Each of the structures shown in FIGS. 5A-5D may be used to provide different coupling ranges, coupling orientations, and/or bandwidth for a respective RF receiver. As a non-limiting example, when the antenna element shown in FIG. 5A is used in a receiver, very small receivers may be designed/built that only couple to the pad 100 in one direction. As another non-limiting example, when the antenna elements shown in FIGS. 5B-5D are used in a receiver, the receiver is then able to couple to the pad 100 in any orientation.

Commonly-owned U.S. patent application Ser. No. 15/29,729 also provides additional examples and descriptions of meandered line patterns for antenna elements (e.g., those shown in FIGS. 2A-2D, 3, 4, 5, 7, 8, and 9A-9B, and described in the specification) and descriptions of the functioning of power transfer systems that include antenna elements with meandered line patterns (e.g., paragraphs [0022]-[0034] and FIGS. 1A-1B), and the disclosure of this commonly-owned application thus supplements the descriptions of antenna elements with meandered line patterns provided herein (for both receivers and transmitters, or a combination thereof).

FIG. 6 is a schematic of an RF charging pad with a plurality of transmitting antenna elements (unit cells) that form a larger RF charging/transmitting pad, in accordance with some embodiments. In some embodiments, the RF charging pad 100 is formed as an array of adjacent antenna elements 120 (the distance between cells may be optimized for the best coverage). In some embodiments, when a receiver is placed in an area/gap that is between adjacent antenna elements 120, attempts to optimize energy transfer (e.g., in accordance with the adaptation scheme discussed above in reference to FIG. 1A) may not result in increased energy transfer above an acceptable threshold level (e.g., 75% or more). As such, in these circumstances, adjacent antenna elements may both be configured to transmit RF waves at full power at the same time to transfer additional energy to a receiver that is placed on a surface of the RF charging pad, and at a location that is between adjacent antenna elements 120.

As one possible configuration in accordance with some embodiments, port (or terminal) group #1 (FIG. 6) supplies power, port (or terminal) groups #2 and #3 provide adaptive loads (e.g., an electromechanical relay moving between short-circuit and open-circuit states). As another example of a suitable configuration, port (or terminal) groups #1, #2 and #3 may also be used to supply power via a power amplifier to the charging pad 100 (at the same time or with one group at a time being switched when necessary).

In some embodiments, each transmitting antenna element 120 of the RF charging pad 100 forms a separate coupling zone which is controlled by a feeding (PA) terminal and one or more terminals to support adaptive load(s), as explained in detail above. In some embodiments, feedback from the receiver helps determine the zone on top of which the receiver is placed, and this determination activates that zone. In circumstances in which the receiver is placed between two or more zones (e.g., at an area/gap that is between adjacent antenna elements 120), additional adjacent zones might be activated to ensure sufficient transfer of energy to the receiver.

The antenna elements 120 described above (e.g., in reference to FIG. 1B) may also be configured to have multiple adaptive load terminals (e.g., multiple adaptive load terminals 121) that are coupled to at different positions along a respective antenna element 120. An example of an antenna element 120 with multiple adaptive load terminals is provided below in reference to FIG. 7. FIG. 7 is a schematic showing a transmitting antenna element (unit cell) with a plurality of adaptive loads (which may be a part of an array of such antennas, as described above in reference to FIGS. 1-6) of an RF charging pad, in accordance with some embodiments. In some embodiments, the RF charging pad 700 includes one or more antenna elements 701 (which may be any of the antenna elements as shown in FIGS. 1B, 2, 4A-4E, 5A-5D, and 6). Each antenna element 701 is powered/fed by a respective power amplifier (PA) switch circuit 708 (which may be a respective one of the PA switch circuits 103 of FIG. 1A) that may be connected to a respective power amplifier 708 or a source of power at a first end of the antenna element 701.

In some embodiments, the input circuit that includes the power amplifier 708 may additionally include a device that can change frequencies of the input signal or a device that can operate at multiple frequencies at the same time, such as an oscillator or a frequency modulator.

In some embodiments, each antenna element 701 of the RF charging pad 700 includes a plurality of respective adaptive load terminals 702, for example, 702 a, 702 b, 702 c, . . . 702 n, at a plurality of positions within a respective antenna element 701. In some embodiments, the antenna element 701 includes a conductive line forming a meandered line pattern (as discussed above in reference to FIGS. 1, 2, and 4-6). In some embodiments, each adaptive load terminals of the plurality of adaptive load terminals 702 for the antenna element 701 is located at different positions on the conductive meandered line of the antenna element 701 as shown in FIG. 7.

In some embodiments, a meandered line antenna element 701 includes a conductive line with multiple turns in one plane. In some embodiments, the multiple turns may be square turns as shown for the antenna element 701 in FIG. 7. In some embodiments, the multiple turns may be round-edged turns. The conductive line may also have segments of varying widths, for example, a segment 706 having a first width, and short-length segment 707 that has a second width that is less than the first width. In some embodiments, at least one of the adaptive load terminals 702 a is positioned at one of the short-length segments (e.g., short-length segment 707) and another adaptive load terminal is positioned anywhere at one of the segments 706 having the first width. In some embodiments, at least one of the adaptive load terminals 702 is positioned or connected anywhere on a width segment, for example, at the middle of a width segment of the meandered line antenna element 701. In some embodiments, the last adaptive load terminal 702 n is positioned at a second end of the conductive line (opposite to a first end at the input terminal 703 of the antenna element 701 described above in reference to FIGS. 1, 2, and 4-6). In some embodiments, in certain design and optimization, an adaptive load terminal is not necessarily positioned at a second end of the meandered line antenna element 701 but can be positioned at any location of the antenna element 701.

In some embodiments, the RF charging pad 700 also includes (or is in communication with) a central processing unit 710 (also referred to here as processor 710). In some embodiments, the processor 710 is configured to control RF signal frequencies and to control impedance values at each of the adaptive load terminals 702, e.g., by communicating with a plurality of the load picks or adaptive loads 712, for example, 712 a, 712 b, 712 c, . . . 712 n, for each of the adaptive load terminals 702 (as discussed above in reference to load pick or adaptive load 106 in FIGS. 1A and 1B).

In some embodiments, an electronic device (e.g., a device that includes a receiver 704 as an internally or externally connected component, such as a remote that is placed on top of a charging pad 700 that may be integrated within a housing of a streaming media device or a projector) and uses energy transferred from one or more RF antenna elements 701 of the charging pad 700 to the receiver 704 to charge a battery and/or to directly power the electronic device.

In some embodiments, the adaptive load terminals 702 at a particular zone or selected positions of the antenna element 701 (e.g., a zone on the antenna element 701 located underneath a position at which an electronic device (with an internally or externally connected RF receiver 704) to be charged is placed on the charging pad) are optimized in order to maximize power received by the receiver 704. For example, the CPU 710 upon receiving an indication that an electronic device with an internally or externally connected RF receiver 704 has been placed on the pad 700 in a particular zone on the antenna element 701 may adapt the plurality of adaptive loads 712, for example, adaptive loads 712 a, 712 b, 712 c, . . . 712 n, that are respectively coupled to the adaptive terminals 702, in order to maximize power transferred to the RF receiver 704. Adapting the set of adaptive loads 712 may include the CPU 710 commanding one or more of the adaptive loads to try various impedance values for one or more of the adaptive load terminals 702 that are coupled to different positions of the antenna element 701. Additional details regarding adapting adaptive loads were provided above, and, for the sake of brevity, are not repeated here.

The effective impedance value (Z_(effective)) at a particular position/portion of the conductive line of the antenna element 701 is affected by a number of variables and may be manipulated by adjusting configurations of the adaptive load terminals 712 that are coupled to various positions on the antenna element 701. In some embodiments, an effective impedance value (Z_(effective)), starting from a point that divides sections 725 (which starts at the terminal 703 of the antenna element 701 and extends to an edge of the receiver 704) and 727 (which is formed by the rest of the transmitting antenna element 701 and the terminal 702 n) and ending at the TX antenna 701's connection to the adaptive load 712 n (e.g., terminal 702 n) will change based on location of the receiver 704 on the TX antenna 701 and based on a set of selected loads provided by adaptive loads 712 at various positions within section 727. In some embodiments, the selected loads are optimized by the adaptive loads 712 (in conjunction with the processor 710) to tune Z_(effective) in such a way that the energy transferred between terminal 703 and the receiver 704 reaches a maximum (e.g., 75% or more of energy transmitted by antenna elements of the pad 700 is received by the RF receiver 704, such as 98%), while energy transfer may also stay at a minimum from terminal 703 to terminal 702 n (e.g., less than 25% of energy transmitted by antenna elements of the pad 700 is not received by the RF receiver 704 and ends up reaching terminals positioned within section 727 or ends up being reflected back, including as little as 2%).

In some embodiments, a selected several adaptive loads 712 of the plurality of adaptive loads 712 are used (by the processor 710) on the antenna element 701 to adjust the impedance and/or frequency of the antenna element 701. In one example, with reference to FIG. 7, only adaptive load terminals 702 a and 702 c are connected at a particular point in time to adaptive loads 712 a and 712 c respectively, while adaptive load terminals 702 b and 702 n are disconnected at the particular point in time. In another example, with reference to FIG. 7, only adaptive load terminals 702 a and 702 n are connected at a particular point in time to adaptive loads 712 a and 712 n, respectively, while adaptive load terminals 702 b and 702 c are disconnected at the particular point in time. In some embodiments, all of the adaptive load terminals 702 are connected at a particular point in time to their respective adaptive loads 712. In some embodiments, none of the adaptive load terminals 702 are connected at a particular point in time to their respective adaptive loads 712. In some embodiments, the impedance value of each of the adaptive loads 712 connected to a selected adaptive load terminal 712 is adjusted individually to optimize the energy transfer.

In embodiments in which a meandered line antenna has been optimized for the multi-band operation, the multiple adaptive load configuration within a single antenna element also enables a broader frequency band adjustment compared with a single adaptive load configuration within a single antenna element as described in FIG. 1B above. The multiple adaptive load configuration within a single antenna element further enhances multiple frequency band operation on a single antenna element. For example, a single antenna element 701 with multiple adaptive load terminals is capable of operating at a wider frequency band than a corresponding antenna element that is configured with one adaptive load terminal.

In some embodiments, adapting the set of adaptive loads 712 also or alternatively includes the CPU 710 causing the set of antenna elements to transmit RF signals at various frequencies until a frequency is found at which a maximum amount of energy is transferred to the RF receiver 704. In some embodiments, for example, one of the antenna elements transmits RF signals at a first frequency, and another one of the antenna elements transmits RF signals at a second frequency that is different from the first frequency. In some embodiments, adjusting the impedance value and/or the frequencies at which the set of antenna elements transmits causes changes to the amount of energy transferred to the RF receiver 704. In this way, the amount of energy transferred to the RF receiver 704 that is maximized (e.g., to transfer at least 75% of the energy transmitted by antenna elements of the pad 700 to the receiver 704, and in some embodiments, adjusting the impedance value and/frequencies may allow up to 98% of the energy transmitted to be received by the receiver 704) may be received at any particular point on the pad 700 at which the RF receiver 704 might be placed.

In some embodiments, the CPU 710 determines that a maximum amount of energy is being transferred to the RF receiver 704 when the amount of energy transferred to the RF receiver 704 crosses a predetermined threshold (e.g., 75% or more of transmitted energy is received, such as up to 98%) or by testing transmissions with a number of impedance and/or frequency values and then selecting the combination of impedance and frequency that results in maximum energy being transferred to the RF receiver 704 (also as described in reference to the adaptation scheme in FIGS. 1A-1D above). In some embodiments, processor 710 is connected to the receiver 704 through a feedback loop (e.g. by exchanging messages using a wireless communication protocol, such as BLUETOOTH low energy (BLE), WIFI, ZIGBEE, infrared beam, near-field transmission, etc, to exchange messages). In some embodiments, the adaptation scheme is employed to test various combinations of impedance values of the adaptive impedance loads 712 and RF frequencies, in order to maximize energy transferred to an RF receiver 704. In such embodiments, each of the adaptive load 712 is configured to adjust the impedance value along a range of values, such as between 0 and infinity. In some embodiments, the adaptation scheme is employed when one or more RF receivers are placed on top of one of the antenna element 701.

In some embodiments, an adaptation scheme is employed to adaptively adjust the impedance values and/or frequencies of the RF signal(s) emitted from the RF antenna(s) 701 of the charging pad 700, in order to determine which combinations of frequency and impedance result in maximum energy transfer to the RF receiver 704. For example, the processor 710 that is connected to the charging pad 700 tries different frequencies (i.e., in the allowed operating frequency range or ranges) by using different selected sets of adaptive loads 712 at different locations of the antenna element 701, e.g. enabling or disabling certain adaptive loads 712, to attempt to adaptively optimize for better performance. For example, a simple optimization either opens/disconnects or closes/shorts each load terminal to ground (in embodiments in which a relay is used to switch between these states), and may also cause RF antenna element 701 to transmit at various frequencies. In some embodiments, for each combination of relay state (open or shorted) and frequency, the energy transferred to the receiver 704 is monitored and compared to energy transferred when using other combinations. The combination that results in maximum energy transfer to the receiver 704 is selected and used to continue to transmitting the one or more RF signals using one or more antenna elements 701 to the receiver 704.

In some embodiments, the single antenna element 701 with multiple adaptive loads 712 of the pad 700 may be configured to operate in two or more distinct frequency bands (such as the ISM bands described above), e.g., a first frequency band with a center frequency of 915 MHz and a second frequency band with a center frequency of 5.8 GHz. In these embodiments, employing the adaptation scheme may include transmitting RF signals and then adjusting the frequency at first predetermined increments until a first threshold value is reached for the first frequency band and then adjusting the frequency at second predetermined increments (which may or may not be the same as the first predetermined increments) until a second threshold value is reached for the second frequency band. In some embodiments, a single antenna element can operate at multiple different frequencies within one or more frequency bands. For example, the single antenna element 701 may be configured to transmit at 902 MHz, 915 MHz, 928 MHZ (in the first frequency band) and then at 5.795 GHz, 5.8 GHz, and 5.805 GHz (in the second frequency band). The single antenna element 701 can operate at more than one frequency bands as a multi-band antenna. A transmitter with at least one antenna element 701 can be used as a multi-band transmitter.

In some embodiments, multiple antenna elements 701 each with multiple adaptive loads 712 may be configured within a particular transmission pad to allow the particular transmission pad to operate in two or more distinct frequency bands respectively at the same time. For example, a first antenna element 701 of the particular transmission pad operates at a first frequency or frequency band, a second antenna element 701 of the particular transmission pad operates at a second frequency or frequency band, and a third antenna element 701 of the particular transmission pad operates at a third frequency or frequency band, and a fourth antenna element 701 of the particular transmission pad operates at a fourth frequency or frequency band, and the four frequency bands are distinct from each other. In this way, the particular transmission pad is configured to operate at multiple different frequency bands.

In some embodiments, the transmitter described herein can transmit wireless power in one frequency or frequency band, and transmit and exchange data with a receiver in another frequency or frequency band.

Different antenna elements operating at different frequencies can maximize energy transfer efficiency when a smaller device is charged with higher frequencies and a larger device is charged with lower frequencies on the same charging pad. For example, devices that require a higher amount of power, such as mobile phones, may also have more space to include larger antennas, thus making a lower frequency of 900 MHz a suitable frequency band. As a comparison, a smaller device, such as an earbud, may require a small amount of power and may also have less space available for longer antennas, thus making a higher frequency of 2.4 or 5.8 GHz a suitable frequency band. This configuration enables more flexibility in the types and sizes of antennas that are included in receiving devices.

Turning now to FIG. 8, in accordance with some embodiments, a flow chart of a method 800 of charging an electronic device through radio frequency (RF) power transmission by using at least one RF antenna with a plurality of adaptive loads is provided. Initially, a charging pad including a transmitter is provided in step 802 that includes at least one RF antenna (e.g., antenna element 701, as described with respect to FIG. 7 above which further includes FIGS. 1-6) for transmitting one or more RF signals or waves, i.e., an antenna designed to and capable of transmitting RF electromagnetic waves. In some embodiments, an array of RF antenna elements 701 are arranged adjacent to one another in a single plane, in a stack, or in a combination of thereof, thus forming an RF charging pad 700 (as described in reference to FIGS. 4A-4E, 5A-5D and 6). In some embodiments, the RF antenna elements 701 each include an antenna input terminal (e.g., the first terminal 703 discussed above in reference to FIG. 7) and a plurality of antenna output terminals (e.g., the plurality of adaptive load terminals 702 discussed above in reference to FIG. 7). In some embodiments, the antenna element 701 includes a conductive line that forms a meandered line arrangement (as shown in FIGS. 1-2, and 4-7). The plurality of adaptive load terminals 702 are positioned at different locations of the conductive line of the antenna element 701.

In some embodiments, the transmitter further comprises a power amplifier electrically coupled between the power input and the antenna input terminal (e.g., PA 708 in FIG. 7). Some embodiments also include respective adaptive loads 712 a, 712 b, 712 c, . . . 712 n electrically coupled to the plurality of antenna output terminals (e.g., adaptive load terminals 702 in FIG. 7). In some embodiments, the transmitter includes a power input configured to be electrically coupled to a power source, and at least one processor (e.g., processor 710 in FIG. 7, and processor 110 in FIGS. 1A-1B) configured to control at least one electrical signal sent to the antenna. In some embodiments, the at least one processor is also configured to control the frequency and/or amplitude of the at least one signal sent to the antenna.

In some embodiments, each RF antenna of the transmitter includes: a conductive line forming a meandered line pattern, a first terminal (e.g., terminal 703) at a first end of the conductive line for receiving current that flows through the conductive line at a frequency controlled by one or more processors, and a plurality of adaptive load terminals (e.g., terminals 702), distinct from the first terminal, at a plurality of positions of the conductive line, the plurality of adaptive load terminals coupled to a respective component (e.g., adaptive loads 712 in FIG. 7) controlled by the one or more processors and that allows for modifying an impedance value of the conductive line. In some embodiments, the conductive line is disposed on or within a first antenna layer of a multi-layered substrate. Also in some embodiments, a second antenna is disposed on or within a second antenna layer of the multi-layered substrate. Finally, some embodiments also provide a ground plane disposed on or within a ground plane layer of the multi-layered substrate.

In some embodiments, a receiver (e.g., receiver 704 in reference to FIG. 7) is also provided (also as described in reference to FIG. 3). The receiver also includes one or more RF antennas for receiving RF signals. In some embodiments, the receiver includes at least one rectenna that converts the one or more RF signals into usable power to charge a device that includes the receiver 704 as an internally or externally connected component (see also steps 304, 306, 310, 314 and 318 in reference to FIG. 3). In use, the receiver 704 is placed within a near-field radio frequency distance to the at least one antenna of the transmitter or the charging pad. For example, the receiver may be placed on top of the at least one RF antenna 701 or on top of a surface that is adjacent to the at least one RF antenna 701, such as a surface of a charging pad 700.

In step 804, one or more RF signals are then transmitted via at the least one RF antenna 701.

The system is then monitored in step 806 to determine the amount of energy that is transferred via the one or more RF signals from the at least one antenna 701 to one or more RF receivers (as is also discussed above). In some embodiments, this monitoring 806 occurs at the transmitter, while in other embodiments the monitoring 806 occurs at the receiver which sends data back to the transmitter via a back channel (e.g., over a wireless data connection using WIFI or BLUETOOTH). In some embodiments, the transmitter and the receiver exchange messages via the back channel, and these messages may indicate energy transmitted and/or received, in order to inform the adjustments made at step 808.

In some embodiments, in step 808, a characteristic of the transmitter is adaptively adjusted to attempt to optimize the amount of energy that is transferred from the at least one RF antenna 701 to the receiver. In some embodiments, this characteristic is a frequency of the one or more RF signals and/or an impedance of the transmitter. In some embodiments, the impedance of the transmitter is the impedance of the adjustable loads. Also in some embodiments, the at least one processor is also configured to control the impedance of the selected set of the plurality of adaptive loads 712. Additional details and examples regarding impedance and frequency adjustments are provided above.

In some embodiments, the at least one processor (e.g. CPU 710 in FIG. 7) dynamically adjusts the impedance of the adaptive load based on the monitored amount of energy that is transferred from the at least one antenna 701 to the RF receiver. In some embodiments, the at least one processor simultaneously controls the frequency of the at least one signal sent to the antenna.

In some embodiments, the single antenna element 701 with multiple adaptive loads 712 of the pad 700 may be dynamically adjusted by the one or more processors to operate in two or more distinct frequency bands (such as the ISM bands described above) at the same time or at different times, e.g., a first frequency band with a center frequency of 915 MHz and a second frequency band with a center frequency of 5.8 GHz. In these embodiments, employing the adaptation scheme may include transmitting RF signals and then adjusting the frequency at first predetermined increments until a first threshold value is reached for the first frequency band and then adjusting the frequency at second predetermined increments (which may or may not be the same as the first predetermined increments) until a second threshold value is reached for the second frequency band. For example, the single antenna element 701 may be configured to transmit at 902 MHz, 915 MHz, 928 MHZ (in the first frequency band) and then at 5.795 GHz, 5.8 GHz, and 5.805 GHz (in the second frequency band). The single antenna element 701 can operate at more than one frequency bands as a multi-band antenna. A transmitter with at least one antenna element 701 can be used as a multi-band transmitter.

In some embodiments, a charging pad or transmitter may include one or more of the antenna element 701 with a plurality of adaptive loads as described in FIG. 7 and one or more antenna element 120 with one adaptive load as described in FIG. 1A-1D.

FIGS. 9A-9D are schematics showing various configurations for individual antenna elements that can operate at multiple frequencies or frequency bands within an RF charging pad, in accordance with some embodiments. As shown in FIGS. 9A-9D, an RF charging pad 100 (FIGS. 1A-1B) or an RF charging pad 700 (FIG. 7) may include antenna elements 120 (FIG. 1B) or 701 (FIG. 7) that configured to have conductive line elements that have varying physical dimensions.

For example, FIGS. 9A-9D show examples of structures for an antenna element that each include a conductive line formed into different meandered line patterns at different portions of the element. The conductive lines at different portions or positions of the element may have different geometric dimensions (such as widths, or lengths, or trace gauges, or patterns, spaces between each trace, etc.) relative to other conductive lines within an antenna element. In some embodiments, the meandered line patterns may be designed with variable lengths and/or widths at different locations of the pad (or an individual antenna element). These configurations of meandered line patterns allow for more degrees of freedom and, therefore, more complex antenna structures may be built that allow for wider operating bandwidths and/or coupling ranges of individual antenna elements and the RF charging pad.

In some embodiments, the antennas elements 120 and 701 described herein may have any of the shapes illustrated in FIGS. 9A-9D. In some embodiments, each of the antenna elements shown in FIGS. 9A-9D has an input terminal (123 in FIG. 1B or 703 in FIG. 7) at one end of the conductive line and at least one adaptive load terminals (121 in FIG. 1B or 702 a-n in FIG. 7) with adaptive loads (106 in FIG. 1B or 712 a-n in FIG. 7) as described above at another end or a plurality of positions of the conductive line.

In some embodiments, each of the antenna elements shown in FIGS. 9A-9D can operate at two or more different frequencies or two or more different frequency bands. For example, a single antenna element can operate at a first frequency band with a center frequency of 915 MHz at a first point in time and a second frequency band with a center frequency of 5.8 GHz at a second point in time, depending on which frequency is provided at an input terminal of each of the antenna elements. Moreover, the shapes of the meandered line patterns shown in FIGS. 9A-9D are optimized to allow the antenna elements to operate efficiently at multiple different frequencies.

In some embodiments, each of the antenna elements shown in FIGS. 9A-9D can operate at two or more different frequencies or two or more different frequency bands at the same time when the input terminal is supplied with more than two distinct frequencies that can be superimposed. For example, a single antenna element can operate at a first frequency band with a center frequency of 915 MHz and a second frequency band with a center frequency of 5.8 GHz at the same time when both frequency bands with a first center frequency of 915 MHz and a second center frequency of 5.8 GHz are supplied at the input terminal of the conductive line. In yet another example, a single antenna element can operate at multiple different frequencies within one or more frequency bands.

In some embodiments, the operating frequencies of the antenna elements can be adaptively adjusted by one or more processors (110 in FIGS. 1A-1B or 710 in FIG. 7) as described above according to the receiver antenna dimension, frequency, or the receiver loads and the adaptive loads on the charging pad.

In some embodiments, each of the antenna elements shown in FIGS. 9A-9D with different meandered patterns at different portions of the conductive line can operate more efficiently at multiple frequencies compared with the more symmetrical meandered line structures (For example, FIG. 1B, 2, 4A-4B, or 6). For example, energy transfer efficiency at different operating frequencies of the antenna elements shown in FIGS. 9A-9D with different meandered patterns at different portions of the conductive line can be improved by about at least 5%, and in some instance at least 60%, more than the more symmetrical meandered line structure elements. For example, the more symmetrical meandered line structure antenna element may be able to transfer no more than 60% of transmitted energy to a receiving device while operating at a new frequency other than a frequency for which the more symmetrical meandered line structure antenna element has been designed (e.g., if the more symmetrical meandered line structure antenna element is designed to operate at 900 MHz, if it then transmits a signal having a frequency of 5.8 GHz it may only be able to achieve an energy transfer efficiency of 60%). In contrast, the antenna element with different meandered patterns (e.g., those shown in FIGS. 9A-9D) may be able to achieve an energy transfer efficiency of 80% or more while operating at various frequencies. In this way, the designs for antenna elements shown in FIGS. 9A-9D ensure that a single antenna element is able to achieve a more efficient operation at various different frequencies.

FIG. 10 is schematic showing an example configuration for an individual antenna element that can operate at multiple frequencies or frequency bands by adjusting the length of the antenna element, in accordance with some embodiments.

In some embodiments as shown in FIG. 10, at least one transmitting antenna element 1002 (as described in FIGS. 1-9) of the one or more transmitting antenna elements of an RF charging pad 1000 has a first conductive segment 1004 (a first portion of a meandered conductive line, such as any of those described above for antenna elements 120 and 701) and a second conductive segment 1006 (a second portion of the meandered conductive line, such as any of those described above for antenna elements 120 and 701). In some embodiments, the first conductive segment includes an input terminal (123 in FIG. 1B or 703 in FIG. 7). In some embodiments, the at least one transmitting antenna element 1002 is configured to operate at a first frequency (e.g., 2.4 GHz) while the first conductive segment 1004 is not coupled with the second conductive segment 1006. In some embodiments, the at least one transmitting antenna element 1002 is configured to operate at a second frequency (e.g., 900 MHz) which is different from the first frequency while the first conductive segment is coupled with the second conductive segment.

In some embodiments, one or more processors (110 in FIGS. 1A-1B or 710 in FIG. 7) are configured to cause coupling of the first segment with the second segment in conjunction with instructing a feeding element (as described as 108 in FIGS. 1A-1B and 708 in FIG. 7) to generate current with a second frequency (e.g., 900 MHz) that is distinct from the first frequency (e.g., 2.4 GHz), thereby allowing the antenna element 1002 to more efficiently operate at the second frequency. The one or more processor may also be configured to cause de-coupling of the second conductive segment from the first conductive segment in conjunction with instructing the feeding element to generate current with the first frequency instead of the second frequency, thereby allowing the antenna element 1002 to more efficiently operate at the first frequency again. In some embodiments, the one or more processors are configured to determine whether to causing the coupling (or de-coupling) of these conductive segments based on information received from a receiver (e.g., RX 104 or 704) that identifies a frequency at which the receiver is configured to operate (e.g., for larger devices with longer receiving antennas, this frequency may be 900 MHz, while for smaller devices with small receiving antennas, this frequency may be 2.4 GHz).

In some embodiments, the coupling described here in FIG. 10 can be implemented by directly connecting two different segments of a single antenna element 1002 while bypassing the conductive line located in-between the two connection points or the two different segments. In some embodiments, coupling can be implemented between more than two different segments of the antenna element 1002. The coupling of the different portions or segments of a single meandered line antenna element 1002 can effectively change the size or length of the conductive line of the antenna element 1002, and therefore enable the single antenna element 1002 to operate at different frequencies. The single antenna element 1002 may also operate at more than one frequency bands as a multi-band antenna.

All of these examples are non-limiting and any number of combinations and multi-layered structures are possible using the example structures described above.

Further embodiments also include various subsets of the above embodiments including embodiments in FIGS. 1-10 combined or otherwise re-arranged in various embodiments, as one of skill in the art will readily appreciate while reading this disclosure.

The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.

It will also be understood that, although the terms “first,” “second,” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first region could be termed a second region, and, similarly, a second region could be termed a first region, without changing the meaning of the description, so long as all occurrences of the “first region” are renamed consistently and all occurrences of the “second region” are renamed consistently. The first region and the second region are both regions, but they are not the same region.

The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 

What is claimed is:
 1. A radio frequency (RF) charging pad, comprising: one or more processors for monitoring an amount of energy that is transferred from the RF charging pad to an RF receiver of an electronic device; and one or more transmitting antenna elements that are configured to communicate with the one or more processors for transmitting RF signals to the RF receiver of the electronic device, each respective transmitting antenna element including: a conductive line forming a meandered line pattern; an input terminal at a first end of the conductive line for receiving current that flows through the conductive line at a frequency controlled by the one or more processors; and a plurality of adaptive load terminals, distinct from the input terminal and distinct from each other, at a plurality of positions of the conductive line, each respective adaptive load terminal of the plurality of adaptive load terminals coupled with a respective component that is configured to be controlled by the one or more processors and is configured to allow modifying a respective impedance value at each respective adaptive load terminal, wherein the one or more processors are configured to adaptively adjust at least one of the frequency and a respective impedance value at one or more of the plurality of adaptive load terminals to optimize the amount of energy that is transferred from the one or more transmitting antenna elements to the RF receiver of the electronic device.
 2. The RF charging pad of claim 1, wherein the frequency is in a first frequency band, and at least one of the one or more transmitting antenna elements is configured to operate at a second frequency band based on adaptive adjustments, by the one or more processors, to respective impedance values at one or more of the plurality of adaptive load terminals of the at least one transmitting antenna element.
 3. The RF charging pad of claim 1, further comprising an input circuit that is coupled with the one or more processors and is configured to provide the current to the input terminal at the first end of the conductive line, wherein the one or more processors are configured to adaptively adjust the frequency by instructing the input circuit to generate the current with a new frequency that is distinct from the frequency.
 4. The RF charging pad of claim 3, wherein the one or more processors are configured to adaptively adjust the frequency by instructing the feeding element to generate the current with a plurality of different frequencies that are determined using predetermined increments.
 5. The RF charging pad of claim 3, wherein: a respective conductive line for at least one of the one or more transmitting antenna elements has a respective meandered line pattern that allows the at least one transmitting antenna element to efficiently transmit RF signals having at least one of the frequency and the new frequency, at least two adjacent segments of the respective conductive line having the respective meandered line pattern have different geometric dimensions relative to each other, and the respective conductive line has a length that remains the same when the at least one transmitting antenna element is configured to transmit RF signals having at least one of the frequency and the new frequency.
 6. The RF charging pad of claim 3, wherein: at least one transmitting antenna element of the one or more transmitting antenna elements has a first segment and a second segment, the first segment including the input terminal, and the at least one transmitting antenna element is configured to: operate at the frequency while the first segment is not coupled with the second segment, and operate at the new frequency while the first segment is coupled with the second segment; and the one or more processors are configured to couple the first segment with the second segment in conjunction with instructing the feeding element to generate the current with the new frequency that is distinct from the frequency.
 7. The RF charging pad of claim 1, wherein the one or more processors are configured to: adaptively adjust at least one of the frequency and a respective impedance value associated with a first transmitting antenna element of the one or more transmitting antenna elements to cause the first transmitting antenna element to operate in a first frequency band, and adaptively adjust at least one of the frequency and the respective impedance value associated with a second transmitting antenna element of the one or more transmitting antenna elements to cause the second transmitting antenna element to operate in a second frequency band, wherein the first frequency band is distinct from the second frequency band.
 8. The RF charging pad of claim 1, wherein the electronic device is placed in contact with or close to a top surface of the RF charging pad.
 9. The RF charging pad of claim 1, wherein the respective component is a mechanical relay coupled with the respective adaptive load terminal for switching the respective adaptive load terminal between open and short states, and the impedance value is adaptively adjusted at the respective adaptive load terminal of the respective transmitting antenna element by opening or closing the mechanical relay to switch between an open or short circuit, respectively.
 10. The RF charging pad of claim 1, wherein the respective component is an application-specific integrated circuit (ASIC), and the respective impedance value is adaptively adjusted by the ASIC to within a range of values.
 11. The RF charging pad of claim 1, wherein the one or more processors are configured to: adaptively adjust at least one of the frequency and the respective impedance value by adaptively adjusting the frequency and a respective impedance value at one or more of the plurality of adaptive load terminals to determine a relative maximum amount of energy that is transferred to the RF receiver of the electronic device, and once the maximum amount of energy is determined, cause each of the one or more transmitting antenna elements to respectively transmit the RF signals at a respective frequency and using a respective impedance value that resulted in the maximum amount of energy transferred to the RF receiver.
 12. The RF charging pad of claim 1, wherein the one or more processors monitor the amount of energy that is transferred to the RF receiver based at least in part on information received from the electronic device, the information identifying energy received at the RF receiver from the RF signals.
 13. The RF charging pad of claim 12, wherein the information received from the electronic device identifying received energy is sent using a wireless communication protocol.
 14. The RF charging pad of claim 13, wherein the wireless communication protocol is bluetooth low energy (BLE).
 15. The RF charging pad of claim 1, wherein the one or more processors monitor the amount of energy transferred based at least in part on an amount of energy that is detected at the respective adaptive load terminal.
 16. A method of charging an electronic device through radio frequency (RF) power transmission, the method comprising: providing a charging pad that includes a transmitter comprising one or more RF antennas, wherein each RF antenna of the one or more RF antennas comprises: a conductive line forming a meandered line pattern; an input terminal at a first end of the conductive line for receiving current that flows through the conductive line at a frequency controlled by one or more processors; and a plurality of adaptive load terminals, distinct from the input terminal and distinct from each other, at a plurality of positions of the conductive line, each respective adaptive load terminal of the plurality of adaptive load terminals coupled with a respective component that is configured to be controlled by the one or more processors and is configured to allow modifying a respective impedance value at each respective adaptive load terminal; transmitting, via the one or more RF antennas, one or more RF signals; monitoring an amount of energy that is transferred via the one or more RF signals from the one or more RF antennas to an RF receiver; and adaptively adjusting a characteristic of the transmitter using the one or more processors of the transmitter to optimize the amount of energy that is transferred from the one or more RF antennas to the RF receiver, wherein the characteristic is selected from a group consisting of (i) a frequency of the one or more RF signals, (ii) an impedance of the transmitter, and (iii) a combination of (i) and (ii), and further wherein the impedance of the transmitter is adaptively adjusted at a respective one or more of the plurality of adaptive load terminals of the one or more RF antennas using the one or more processors of the transmitter.
 17. The method of claim 16, wherein the frequency is in a first frequency band, and at least one of the one or more RF antennas is configured to operate at a second frequency band based on adaptive adjustments, by the one or more processors, to respective impedance values at one or more of the plurality of adaptive load terminals of the at least one RF antenna.
 18. The method of claim 16, wherein: a respective conductive line for at least one of the one or more RF antennas has a respective meandered line pattern that allows the at least one RF antenna to efficiently transmit the one or more RF signals having at least one of the frequency and a new frequency, at least two adjacent segments of the respective conductive line having the respective meandered line pattern have different geometric dimensions relative to each other, and the respective conductive line has a length that remains the same when the at least one RF antenna is configured to transmit the one or more RF signals having at least one of the frequency and the new frequency.
 19. The method of claim 16, wherein: at least one RF antenna of the one or more RF antennas has a first segment and a second segment, the first segment including the input terminal, and the at least one RF antenna is configured to: operate at the frequency while the first segment is not coupled with the second segment, and operate at a new frequency while the first segment is coupled with the second segment; and the one or more processors are configured to couple the first segment with the second segment in conjunction with instructing a feeding element at the input terminal to generate the current with the new frequency that is distinct from the frequency.
 20. A non-transitory computer-readable storage medium comprising executable instructions that, when executed by one or more processors that are coupled with a radio frequency (RF) charging pad that includes one or more transmitting antenna elements, cause the one or more processors to: monitor an amount of energy that is transferred from the RF charging pad to an RF receiver of an electronic device; communication with the one or more transmitting antenna elements for transmitting RF signals to the RF receiver of the electronic device, each respective transmitting antenna element including: a conductive line forming a meandered line pattern; an input terminal at a first end of the conductive line for receiving current that flows through the conductive line at a frequency controlled by the one or more processors; and a plurality of adaptive load terminals, distinct from the input terminal and distinct from each other, at a plurality of positions of the conductive line, each respective adaptive load terminal of the plurality of adaptive load terminals coupled with a respective component that is configured to be controlled by the one or more processors and is configured to allow modifying a respective impedance value at each respective adaptive load terminal; and adaptively adjust at least one of the frequency and a respective impedance value at one or more of the plurality of adaptive load terminals to optimize the amount of energy that is transferred from the one or more transmitting antenna elements to the RF receiver of the electronic device. 